Bypass Mode - Eaton 93PM Installation And Operation Manual

Understanding UPS Operation
Bypass Input
Rectifier Input
Rectifier
Switchgear
Figure 5-3. Path of Current Through the UPS in Normal Mode
5.2.4

Bypass Mode

The critical load is not protected from voltage or frequency fluctuations or power outages while
the UPS is in Bypass mode.
The UPS automatically switches to Bypass mode if it detects an overload, load fault, or internal failure. The UPS
can also be transferred from Normal mode to Bypass mode manually. The bypass source supplies the
commercial AC power to the load directly. Figure 5-4 shows the path of electrical power through the UPS
system when operating in Bypass mode.
In Bypass mode, the output of the system is provided with three-phase AC power directly from the system
input. While in this mode, the output of the system is not protected from voltage or frequency fluctuations or
power outages from the source. Some power line filtering and spike protection is provided to the load but no
active power conditioning or battery support is available to the output of the system in the Bypass mode of
operation.
The internal bypass is comprised of a solid-state, silicon-controlled rectifier (SCR) continuous static switch, and
bypass switchgear. The static switch is used instantaneously anytime the inverter is unable to support the
applied load. The continuous static switch is wired in series with the bypass switchgear, and together they are
wired in parallel with the rectifier and inverter.
The static switch, being an electronically-controlled device, can be turned on immediately to pick up the load
from the inverter while the inverter switchgear opens to isolate the inverter. The bypass switchgear is normally
closed, ready to support the static switch unless the bypass input source becomes unavailable.
If the UPS transfers to Bypass mode from Normal mode due to any reason other than operator intervention,
the UPS automatically attempts to transfer back to Normal mode (up to three times within a ten minute period).
The fourth transfer locks the critical load to the bypass source and requires operator intervention to transfer.
5-4 Eaton 93PM UPS (60–100 kW, 480V) Installation and Operation Manual P-164000227—Rev 2
Bypass Switchgear
Rectifier
Switchgear
Closed
Open
Static
Switch
Inverter
Battery Converter
Battery
Switchgear
Battery
CAUTION
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Output
Inverter
Switchgear
Main Power Flow
Trickle Current
Energized
De-Energized